The practice of donating and transplanting bone tissue is beginning to form an important part of therapy for a number of ailments involving bone.
FIG. 1 is a three-dimensional diagram showing the appearance of both a cross and a longitudinal section of an example of a bone structure, and shows various components of the bone. Of course, FIG. 1 is not as detailed as possible, and does not feature every element of bone tissue. The purpose of FIG. 1 is only to briefly show some features of natural bone which also occur in the bone composites of the present invention. With respect to FIG. 1, a bone 10 section is shown. Lamellae 15 are shown within the bone cross section. The haversian canals 20 are shown. In the longitudinal section of the drawing, blood vessels 25 are shown in connection with the haversian canals 20. Finally, the marrow portion 30 is shown with blood vessels 25 extending into the marrow portion of the bone.
Tissue grafting of living tissue from the same patient, including bone grafting, is well known in medical science. Tissue such as bone is removed from one part of a body (the donor site) and inserted into tissue in another (the host site) part of the same (or another) body. This method has been desirable in the past because the tissue was believed to be highly osteoconductive. With respect to living bone tissue, it has been desirable in the past to be able to remove a piece of living tissue graft material which is the exact size and shape needed for the host site where it will be implanted, but it has often proved very difficult to achieve this goal.
Until recently, developers of bone transplants and prostheses have believed that it is desirable to maintain graft tissue in a living state during the grafting process. It is relatively undisputed that the use of living tissue in a graft will promote bone healing, but recent surgical experience has shown that healing can be achieved with allografts of non-living bone material which has been processed.
Processing of bone material which does not contain living tissue is becoming more and more important. Non-living bone grafting techniques have been attempted both for autografts and for allografts. The use of autograft bone is where the patient provides the source of the bone, and the use of allograft bone is where another individual of the same species provides the source of the bone.
In the prior art, transplanted bone has been used in the past to provide support, promote healing, fill bony cavities, separate bony elements (such as vertebral bodies), promote fussion (where bones are induced to grow together in a single, solid mass), or stabilize the sites of fractures.
For example, Nashef U.S. Pat. No. 4,678,470 discloses a method of creating bone graft material by machining a block of bone to a particular shape or by pulverizing and milling it. The graft material is then tanned with glutaraldehyde to sterilize it. This process can produce bone plugs of a desired shape.
In the Nashef process, the process of pulverizing or milling the bone material destroys the structure of the bone tissue. The step of tanning it with glutaraldehyde then renders the graft material completely sterile.
It is now possible to obtain allograft bone which has been processed to remove all living material which could present a tissue rejection problem or an infection problem. Such processed material retains much of the mineral quality of the original living bone, rendering it more osteoinductive. Moreover, it can be shaped according to known and new methods to attain enhanced structural behavior. In fact spine surgeons express a distinct preference for such materials, and at least one supplier, the Musculoskeletal Transplant Foundation (MTF), has introduced femoral ring allografts for spine surgeries.
Research shows that such allografts are very favorable for spinal surgery. According to Brantigan, J. W., Cunningham, B. W., Warden, K., McAfee, P. C., and Steffee, A. D., A compression Strength of Donor Bone for Posterior Lumbar Interbody Fusion, Spine, Vol. 18, No. 9, pp. 12113–21 (July 1993):
Many authors have viewed donor bone as the equivalent of autologous bone. Nasca, et al . . . compared spinal fusions in 62 patients with autologous bone and 90 patients with cryopreserved bone and found successful arthrodesis in 87% of autologous and 86.6% of allograft patients. (Citations omitted.).
A drawback of fabricating transplants and prostheses from donated allograft is that the process necessitates discard of a great deal of scrap and powdered bone material. Good quality donated bone is a scarce resource, so that devising a method of using scrap and powdered allograft bone material would be of great assistance to this highly beneficial endeavor. The present invention uses ground bone to make solid shapes. The results of the present invention are superior to the prior art processes and the process and composite of the present invention allows for a greater amount of donor bone to become available. For example, with the present invention, bone can now be used from older donors. With a transplanted allograft, older bone may be too brittle and weak.
In the fabrication of bone transplants, it was observed that bone material which yields to compressive loads at the exterior surfaces without significant degradation of the interior structural properties, such as cancellous or trabecular bone, can be shaped. It is not unusual that reshaping of a graft tissue is necessary to obtain the best possible graft. In particular, bone tissue may be stronger and better able to bear force when it is denser and more compact.
Additionally, prior art techniques have a serious limitation in that bone parts and bone products made from allograft cortical tissue may be limited in size, dimension and shape because of the anatomical limits on the thickness and length of the source bone. With the method of the present invention, many shapes and forms can be fabricated from allograft cortical bone tissue including pins, screws, plates, intervertebral discs, and the like for use in surgery.
Allograft bone occurs in two basic forms: cancellous bone (also referred to as trabecular bone) and cortical bone. Cortical bone is highly dense and has a compound structure comprised of calcium hydroxyapatite reinforced with collagen fiber. In the present invention, cortical bone tissue is preferred.
Compression of allograft bone is desirable from general considerations. Generally, bone samples are stronger when they are more dense. Compressing allograft bone increases its density and thus generally strengthens the allograft. In addition, recent studies have indicated that the shell of vertebral bone is very much like condensed trabecular bone. Mosekilde, L., A Vertebral structure and strength in vivo and in vitro, Calc. Tissue Int. 1993;53 (Suppl):121–6; Silva, M. J., Wang, C., Keaveny, T. M., and Hayes, W. C., A Direct and computed tomography thickness measurements of the human lumbar vertebral shell and endplate, Bone 1994:15:409–14; Vesterby, A., Mosekilde, L., Gunderson, H. J. G., et al., Biologically meaningful determinants of the in vitro strength of lumbar vertebrae, Bone 1991;12:219–24.
Compression also allows conversion of larger irregular shapes into the desirable smaller shape, thereby permitting more disparate sources of allograft bone to be used. By compressing bone to a given shape it is possible to configure the allograft to match a preformed donee site prepared by using a shaped cutter to cut a precisely matching cut space. In particular, this method of formation facilitates the formation of match mated surfaces of the implant for the formation of a particular shape for skeletal repair or revision.
For the reasons stated above, in certain embodiments of the present invention, compression is useful as part of the molding step in forming the bone composites of the present invention. However, an advantage of the present invention is that in some embodiments compression is not required, and in some embodiments it is preferred—but at very low pressure when compared to the compression levels of the prior art.
It is known that allograft bone can be reshaped into one of many configurations for use as an implant. Various methods, including that of Bonutti, U.S. Pat. Nos. 5,662,710 and 5,545,222, can be used to shape allograft material into the desired shape.
A goal of a bone composite transplant is that the transplant is readily received and hosted by the receiving mammal, with bone fusion occuring (i.e., the composite should be biocompatible and osteoinductive). Today, the only other osteoinductive implants are allograft shapes that have been cut and shaped from cadaver donated bone. This method has serious drawbacks in that it is difficult for sufficient fusion to take place and the implant usually lacks sufficient structural strength and density.
U.S. Pat. No. 6,025,538 to Yaccarino, III, discloses allograft bone devices for surgical implantation in the bone tissue.
U.S. Pat. No. 5,439,864 to Pruitt, et al., discloses shaped demineralized bone for use in the surgical repair of bone defects.
U.S. Pat. No. 5,662,710 to Bonutti, discloses a tissue press for shaping or compressing a piece of graft tissue.
U.S. Pat. No. 5,899,939 to Boyce et al. discloses a bone-derived implant that comprises cortical bone and is used to repair, replace, or augment various portions of animal and human skeletal systems. The bone implant of this invention is made up as individual layers that may be held together by adhesives. Finally, the bone-derived implant of this invention may have one or more cavities which may be filed with demineralized bone powder. This patent fails to disclose making an implant or prosthesis from ground bone powder.
U.S. Pat. No. 6,025,538 to Yaccarino, III discloses allograft bone devices for surgical implantation in the bone tissue. The device is larger than the natural dimensions of a cortical bone layer and is made by combining two or more smaller pieces to form a compound bone structure. A pin may be placed through the component bone members of the bone structure. Finally, each bone member is shaped to form a groove to receive the end of the other bone member. The device of this invention may be processed to form compound bone pins, bone screws, plates, disks, wedges, blocks, etc. The devices may be secured together by using any surgical bone adhesive with a synthetic absorbable or non-absorbable polymer in connection with the pin that connects the two bone pieces together.
U.S. Pat. No. 6,090,998 to Grooms et al. discloses a unitary bone implant having at least one rigid, mineralized bone segment. The implant may be machined to include threads, grooves, etc. to provide a means for fixation of the implant directly to a bone machined in a complimentary fashion. The implant of this invention may be used to repair or replace ligaments, tendons, and joints.
U.S. Pat. No. 6,045,554 to Grooms et al. discloses an interference screw manufactured from cortical allograft bone tissue may be used as a fixation screw for cruciate ligament graphs. The screw is made by obtaining a fragment of bone from the cortex and machining the thread, tip and drive head of the screw. More specifically, the section is removed from a femur or tibia, a dowel of the tissue is machined. The machining may be done by a grinding wheel.
U.S. Pat. No. 5,507,813 to Dowd et al. discloses a process for making surgically implantable materials fabricated from elongate bone particles. The particles may be graded into different sizes. Additionally, the particles are described as filaments, fibers, threads, slender or narrow strips, etc. The elongate bone particles may be mixed with an adhesive and/or filler. The fillers include bone powder.
U.S. Pat. No. 5,061,286 to Lyle discloses an osteoprosthetic implant with demineralized bone powder attached thereto. The bone powder apparently provides an osteogenic coating for the prosthesis. This coating allows the prosthesis to be firmly anchored to the bone repair site. The prosthesis device may be polymeric. The bone particles may be adhere to the prosthetic device and each other by a binder. Cyanoacrylate is disclosed as one of the binders.
U.S. Pat. No. 5,516,532 to Atala et al. discloses a method of making a cartilage and bone preparation using ground bone. The ground bone is apparently mixed with polymeric carriers and provides a suspension that may be injectable and used for correction of a variety of tissue defects. The suspension is typically injected through a cystoscopic needle or via a syringe directly into a specific area where the bulking is required.
U.S. Pat. No. 6,136,029 to Johnson et al. discloses an open-celled article that is useful as a bone substitute material that is highly porous and is of low density. The article comprises a framework that is preferably ceramic.
U.S. Pat. No. 6,294,187 to Boyce, et al. discloses an osteoimplant for use in the repair, replacement, and/or augmentation of various portions of animal or human skeletal systems. The implant of this patent comprises bone particles in combination with one or more biocompatible components. The implant is made by applying compressive force of at least 1,000 psi to the composition.
U.S. Pat. No. 5,565,502 to Glimcher, et al. discloses a process for removing and isolating the calcium-phosphate crystals of bone. The bone powder is prepared by milling bone in liquid nitrogen and sieving to a particle size ranging up to approximately 20 microns. The bone particles are then suspended in an organic solvent. The purified calcium-phosphate crystals are isolated from the bone and are useful as an aid to induce and promote bone healing.
U.S. Pat. No. 5,824,078 to Nelson, et al. discloses an allograft bone press. The bone press is used to compress cancellous bone chips to conform to a shape of a mold.
U.S. Pat. No. 4,645,503 to Lin, et al. discloses moldable bone-implant material. This material is prepared by mixing hard bone-graft filler particles with a biocompatible thermoplastic binder.
U.S. Pat. No. 4,843,112 to Gerhart, et al. discloses a moldable, biocompatible, polyester-particulate composite that can be used for reinforcement of fractures in a bone. This invention is directed to a biodegradable cement composition adapted for use in the surgical repair of living bone and for the controlled-released delivery of pharmaceutical agents.
U.S. Pat. No. 6,132,472 to Bonutti discloses a tissue press for shaping or compressing a piece of tissue. This apparatus and method is designed to press or shape tissue while preserving the tissue alive.
In response to the need for a composite material to make use of bone fragments and bone powder for fabricating implants and prosthetic devices for bone the current inventor developed the present invention.